1. Technical Field of the Invention
The present invention relates generally to an angular position sensor working to measure an angular position of a rotary member, and more particularly to an improved structure of such an angular position sensor designed to sense a magnetic flux density that is higher in linearity.
2. Background Art
Typical angular position sensors working to measure an angular position of a rotary shaft are made up of a ring-shaped magnet with an N-pole and an S-pole arrayed in a circumferential direction thereof, a magnetic yoke disposed around the periphery of the magnet, and magnetic sensors. The magnetic yoke has formed therein radial grooves forming air gaps. The magnetic sensors are disposed within the air gaps and work to measure magnetic flux densities in the air gaps. For instance, U.S. Pat. No. 5,528,139 to Oudet et al., issued Jun. 18, 1996 (corresponding to Japanese Patent No. 2842482) teaches such a type of angular position sensor.
The N-pole and the S-pole of the magnet are disposed at an angular interval of 180° and create a magnetic flux density changing at a constant rate in the circumferential direction of the magnet. This causes the magnetic flux density as measured by the magnetic sensors to change in the form of a sine wave upon rotation of the rotary shaft. It is, thus, impossible for the magnetic sensors to measure the magnetic flux density that is higher in linearity. Determination of an absolute angular position of the rotary shaft requires large-scaled operations on trigonometric functions and/or using a map, thus posing the problem that the operation load on the system is undesirably high.